Many naturally occurring, biologically active compounds are proteins or peptides based upon xcex1-amino acids (i.e. sequences of xcex1-amino acids in which the xcex1-carboxyl group of one amino acid is joined by an amide bond to the xcex1-amino group of the adjacent amino acid). In recent years an approach to the discovery of new pharmaceutically active drugs has been to synthesise libraries of peptides and then to assay for compounds within the library which have a desired activity, such as a desired binding activity. However, xcex1-amino acid peptides are not altogether satisfactory for pharmaceutical uses, in particular because they are often poorly absorbed and subject to proteolytic degradation in vivo.
We have now synthesised new peptides based on xcex2-amino acids and have found that these peptides have unexpected and desirable properties.
Accordingly the present invention provides a xcex2-peptide comprising 2 or more different xcex2-amino acid residues.
For the purposes of the present description a xcex2-peptide comprises a sequence of 2 or more xcex2-amino acid residues in which the xcex1-carboxyl group of one amino acid is joined by an amide bond to the xcex2-amino group of the adjacent amino acid. The xcex2-peptides of the invention may comprise any number of amino acid residues, though conveniently comprise from 2 to 11, preferably from 4 to 7, especially 5 or 6, xcex2-amino acid residues.
The xcex2-amino acid residues of the xcex2-peptides of the invention are characteristically xcex2-amino-n-propionic acid derivatives, typically further substituted at the xcex1- and/or xcex2-carbon atoms and may be further substituted, e.g. at the N-terminal amino nitrogen atom. The xcex1-, xcex2- and and amino substituents may include substituents containing from 1 to 43 carbon atoms optionally interrupted by up to 4 hetero atoms, selected from O, N or S, optionally containing a carbonyl (i.e. xe2x80x94C(O)xe2x80x94) group, and optionally further substituted by up to 6 substituents selected from halo, NO2, xe2x80x94OH, C1-4alkyl, xe2x80x94SH, xe2x80x94SO3, xe2x80x94NH2, C1-4acyl, C1-4acyloxy, C1-4alkylamino, C1-4dialkylamino, trihalomethyl, xe2x80x94CN, C1-4alkylthio, C1-4alkylsulfinyl, or C1-4alkylsulfonyl. Conveniently, the xcex1-, xcex2- and amino substituents may include any of those substituents defined below as the xe2x80x9cRxe2x80x9d substituents of formula I. For example, the xcex1- and xcex2-substituents may be selected from the group comprising the substituents which are present on the xcex1-carbon atoms of xcex1-amino acids, e.g. xe2x80x94H, xe2x80x94CH3, xe2x80x94CH(CH3)2, xe2x80x94CH2xe2x80x94CH(CH3)2, xe2x80x94CH(CH3)CH2CH3, xe2x80x94CH2-phenyl, CH2-pOH-phenyl, xe2x80x94CH2-indole, xe2x80x94CH2xe2x80x94SH, xe2x80x94CH2xe2x80x94CH2xe2x80x94Sxe2x80x94CH3, xe2x80x94CH2OH, xe2x80x94CHOHxe2x80x94CH3, xe2x80x94CH2xe2x80x94CH2xe2x80x94CH2xe2x80x94CH2xe2x80x94NH2, xe2x80x94CH2xe2x80x94CH2xe2x80x94CH2xe2x80x94NHxe2x80x94C(NH)NH2, xe2x80x94CH2-imidazole, xe2x80x94CH2xe2x80x94COOH, xe2x80x94CH2xe2x80x94CH2-COOH, xe2x80x94CH2xe2x80x94CONH2, xe2x80x94CH2xe2x80x94CH2-CONH2 or together with an adjacent xe2x80x94NH group forms a proline amino acid residue.
The xcex2-peptides of the invention preferably comprise only xcex2-amino acid residues. However, the invention includes xcex2-peptides, for instance longer xcex2-peptides, e.g. comprising 7 or more acid residues, which contain one or a few, e.g. 1 or 2, acid residues which are not xcex2-amino acids, e.g. xcex1- or xcex3-amino acids, or an xcex1-, xcex2- or xcex3-hydroxycarboxlic acids. For example, a non-xcex2-amino acid may be present in the xcex2-peptide at a junction or transition region between two sequences of xcex2-amino acid residues.
Characteristically substitutents present on the xcex1- and/or xcex2-carbon atoms of the xcex2-amino acid residues are in the radial orientation with respect to the peptide chain.
Preferably the present invention provides a compound of formula I 
wherein
each R is H, xe2x80x94R5, xe2x80x94OR5, xe2x80x94C(O)R5, xe2x80x94R5C(O)R6, xe2x80x94C(O)OR5, xe2x80x94R5C(O)OR6, xe2x80x94R5OC(O)R6, xe2x80x94R5OC(O)OR6, xe2x80x94R5NR6C(O)R7, xe2x80x94R5C(O)NR6R7, xe2x80x94C(O)NR6R7, xe2x80x94R5OC(O)NR6R7, xe2x80x94R5NR6C(O)NR7R8, xe2x80x94R5NR6C(O)OR7, xe2x80x94R5xe2x80x94Oxe2x80x94R6, xe2x80x94R5xe2x80x94NR6R7, xe2x80x94R5xe2x80x94Sxe2x80x94R6, xe2x80x94R5SOmxe2x80x94R6, xe2x80x94R5OR6xe2x80x94Oxe2x80x94R7, xe2x80x94R5NR6R7xe2x80x94Oxe2x80x94R8, xe2x80x94R5SOmR6xe2x80x94Oxe2x80x94R7, xe2x80x94C(O)R5xe2x80x94Oxe2x80x94R6, xe2x80x94C(O)OR5xe2x80x94Oxe2x80x94R6, xe2x80x94R5C(O)R6xe2x80x94Oxe2x80x94R7, xe2x80x94R5C(O)OR6xe2x80x94Oxe2x80x94R7, xe2x80x94R5OC(O)R6xe2x80x94Oxe2x80x94R7, xe2x80x94R5OC(O)OR6xe2x80x94Oxe2x80x94R7, xe2x80x94R5NR6C(O)R7xe2x80x94Oxe2x80x94R8, xe2x80x94C(O)NR5R6xe2x80x94Oxe2x80x94R7, xe2x80x94R5C(O)NR6R7xe2x80x94Oxe2x80x94R8, xe2x80x94R5OC(O)NR6R7xe2x80x94Oxe2x80x94R8, xe2x80x94R5NR6C(O)NR7R8xe2x80x94Oxe2x80x94R9, xe2x80x94R5NR6C(O)OR7xe2x80x94Oxe2x80x94R8, xe2x80x94R5OR6xe2x80x94Sxe2x80x94R7, xe2x80x94R5NR6R7xe2x80x94Sxe2x80x94R8, xe2x80x94R5SOmR6xe2x80x94Sxe2x80x94R7, xe2x80x94C(O)R5xe2x80x94Sxe2x80x94R6, xe2x80x94C(O)OR5xe2x80x94Sxe2x80x94R6, xe2x80x94R5C(O)R6xe2x80x94Sxe2x80x94R7, xe2x80x94R5C(O)OR6xe2x80x94Sxe2x80x94R7, xe2x80x94R5OC(O)R6xe2x80x94Sxe2x80x94R7, xe2x80x94R5OC(O)OR6xe2x80x94Sxe2x80x94R7, xe2x80x94R5NR6C(O)R7xe2x80x94Sxe2x80x94R8, xe2x80x94C(O)NR5R6xe2x80x94Sxe2x80x94R7, xe2x80x94R5C(O)NR6R7xe2x80x94Sxe2x80x94R8, xe2x80x94R5OC(O)NR6R7xe2x80x94Sxe2x80x94R8, xe2x80x94R5NR6C(O)NR7R8xe2x80x94Sxe2x80x94R9, xe2x80x94R5NR6C(O)OR7xe2x80x94Sxe2x80x94R8, xe2x80x94R5OR6xe2x80x94NR7R8, xe2x80x94R5NR6R7xe2x80x94NR8R9, xe2x80x94R5SOmR6xe2x80x94NR7R8, xe2x80x94C(O)R5xe2x80x94NR6R8, xe2x80x94C(O)OR5xe2x80x94NR6R8, xe2x80x94R5C(O)R6xe2x80x94NR7R8, xe2x80x94R5C(O)OR6xe2x80x94NR7R8, xe2x80x94R5OC(O)R6xe2x80x94NR7R8, xe2x80x94R5OC(O)OR6xe2x80x94NR7R8, xe2x80x94R5NR6C(O)R7xe2x80x94NR8R9, xe2x80x94C(O)NR5R6xe2x80x94NR7R8, xe2x80x94R5C(O)NR6R7xe2x80x94NR8R9, xe2x80x94R5OC(O)NR6R7xe2x80x94NR8R9, xe2x80x94R5NR6C(O)NR7R8xe2x80x94NHR9 or xe2x80x94R5NR6C(O)OR7xe2x80x94NR8R9xe2x80x2,
where R5, R6, R7, R8 and R9 are each independently C1-10alkyl, C1-10alkenyl, C1-10alkynyl, C6-10aryl, C6-14aralkyl, C6-14aralkenyl or C6-14aralkynyl and m is 1,2,3 or 4; and where R5 R6, R7, R8 and R9 are each unsubstituted or substituted with up to 6 substituents selected from halo, NO2, xe2x80x94OH, C1-4alkyl, xe2x80x94SH, xe2x80x94SO3, xe2x80x94NH2, C1-4acyl, C1-4acyloxy, C1-4alkylamino, C1-4dialkylamino, trihalomethyl, xe2x80x94CN, C1-4alkylthio, C1-4alkylsulfinyl, or C1-4alkylsulfonyl, provided that all the R substituents are not identical, or R forms a cyclic structure , e.g. a carbocyclic or heterocyclic ring, with itself, with R3 or with the carbonyl group attached to the immediately adjacent nitrogen atom;
R1 and R2, which may be the same or different, are H, an N-protecting group or as defined above for R, or R1 and R2 are linked together in a 3 to 7 membered heterocyclic ring structure, or either R1 or R2 together with OX signify an amide bond;
each R3, which may be the same or different, is as defined above for R, or R3 forms a cyclic structure , e.g. a carbocyclic or heterocyclic ring, with itself, with R or with the nitrogen atom of its xcex2-amino acid residue,
provided that R and R3 are not both H;
X is H, an O-protecting group or as defined above for R, except that X is not xe2x80x94OR5, or OX together with R1 or R2 signify an amide bond;
n is 1,2,3,4,5,6,7,8,9, or 10.
The xcex2-peptides of the invention, and in particular the compounds of formula I, are hereinafter referred to as the compounds of the invention.
Characteristically when R and R3 are not H, R and R3 are in the radial orientation with respect to the peptide chain.
Typically when R or R3 form a cyclic structure, the cyclic structure is a 3 to 7 membered cyclic structure.
Preferably n is 4, 5, 6 or 7 or more preferably n is 5 or 6.
Thus in preferred embodiments the invention provides a compound of formula II or a compound of formula III 
wherein R, R1, R2, R3 and X are as defined above.
When R1 and R2 are linked together in a ring structure the structure is optionally substituted as for R5 etc. above and may be fused with one or more rings such as phenyl rings. For example the R1 and R2 ring system may be a piperidine or pyridine ring system.
When either R1 or R2 together with OX signify an amide bond, i.e. when the compounds of formula I are cyclic compounds, n is preferably at least 2.
In the present description unless otherwise indicated terms such as xe2x80x9ccompounds of the inventionxe2x80x9d embrace the compounds in salt form as well as in free base form and also when the compounds are attached to a solid phase. Where a basic substituent such as an amine substituent is present, the salt form may be a double acid addition salt, for example a dihydrochloride.
The term halogen includes F, Cl, Br and I, preferably F and Cl.
Suitable N-protecting groups as R1 or R2 include groups of formula H(CH2CH2O)pxe2x80x94 where p=3-30; R10COxe2x80x94; R11OCOxe2x80x94 or R12SO2xe2x80x94,
in which R10 is C1-4 alkyl or H(CH2xe2x80x94Oxe2x80x94CH2)p wherein p is defined as above;
R11 is C1-6 alkyl, phenyl, benzyl or naphthyl; and R12 is phenyl, naphthyl, or C1-4 alkylphenyl;
of which R11OCOxe2x80x94 is particularly preferred, especially when R11 is tert. butyl (i.e. Boc as the protecting group), or when R11 is benzyl (i.e. the protecting group customarily designated as Z).
Suitable O-protecting groups as X include are alkyl, e.g. C1-4 alkyl, groups or aromatic groups, e.g. benzyl, including substituted phenyl groups such pentafluorophenyl.
In a particular embodiment the compounds of formula I are peptides of xcex2-amino acids which are unsubstituted at the xcex1-carbon atom, i.e. compounds of formula IV 
wherein R, R1, R2, X and n are as defined above.
xcex2-amino acids which are unsubstituted at the xcex1-carbon atom and the corresponding peptides of formula IV are conveniently referred to as xcex23 amino acids and xcex23 peptides respectively.
In a further particular embodiment the compounds of formula I are peptides of xcex2-amino acids which are unsubstituted, apart from amino substituted, at the xcex2-carbon atom, i.e. compounds of formula V 
wherein R1, R2, R3, X and n are as defined above.
xcex2-amino acids which are unsubstituted, apart from the amino substitituent, at the xcex2-carbon atom and the corresponding peptides of formula V are conveniently referred to as xcex22 amino acids and xcex22 peptides respectively.
In further particular embodiments the compounds of the invention comprise a mixture of xcex22- and xcex23-amino acids; for instance, as alternating xcex22- and xcex23-amino acids or as discrete stretches of xcex22-amino acids linked to discrete stretches of xcex23-amino acids.
The substituents R, R1, R2, R3 and X have many possible significations as indicated above. Conveniently, however, in particular embodiments the substituents R, R1, R2, R3 and X may be selected from the group comprising the substituents which are present on the xcex1-carbon atoms of xcex1-amino acids, e.g. xe2x80x94H, xe2x80x94CH3, xe2x80x94CH(CH3)2, xe2x80x94CH2xe2x80x94CH(CH3)2, xe2x80x94CH(CH3)CH2CH3, xe2x80x94CH2phenyl, CH2xe2x80x94pOH-phenyl, xe2x80x94CH2-indole, xe2x80x94CH2xe2x80x94SH, xe2x80x94CH2xe2x80x94CH2xe2x80x94Sxe2x80x94CH3, xe2x80x94CH2OH, xe2x80x94CHOHxe2x80x94CH3, xe2x80x94CH2xe2x80x94CH2xe2x80x94CH2xe2x80x94CH2xe2x80x94NH2, xe2x80x94CH2xe2x80x94CH2xe2x80x94CH2xe2x80x94NHxe2x80x94C(NH)NH2xe2x80x94CH2-imidazole, xe2x80x94CH2xe2x80x94COOH, xe2x80x94CH2xe2x80x94CH2xe2x80x94COOH, xe2x80x94CH2xe2x80x94CONH2, xe2x80x94CH2xe2x80x94CH2xe2x80x94CONH2 or together with an adjacent xe2x80x94NH group forms a proline amino acid residue.
In accordance with the present invention it has been found that the compounds of the invention have desirable properties. For example, compounds of formula I in which n is 5 or 6 are able to form stable helix structures in solution, in contrast to xcex1-peptides for which distinct secondary structures are observed in solution only when the peptide comprises at least 15 to 20 amino acid residues. Thus it has been found that representative compounds of formula I comprising L-xcex2-amino acids form compact, left-handed or (M) 31 helices of 5 xc3x85 pitch. Representative compounds of formula I comprising D-xcex2-amino acids form corresponding compact, right-handed helices. The corresponding helices formed by xcex1-peptides of L-amino acids are right-handed 3.613 xcex1-helices with a pitch of 5.6 xc3x85. Other structures of the compounds of the invention are discussed hereinafter and in the references referred to hereinafter.
In view of their structure and in preferred embodiments xcex2-peptides of the invention, especially xcex2-hexapeptides, may be used as xcex2-turn mimetics.
Generally also the compounds of the invention have much greater stability to the action of peptidases, such as pepsin, than xcex1-peptides. As such the compounds of formula may conveniently exhibit correspondingly longer half lives, e.g. serum half lives, in vivo than than xcex1-peptides.
In formula I above the carbon atoms marked with an asterisk (*) may be optically active centres, i.e. when R and R3 are not H, and may be in the R or the S configuration. Thus the invention includes the compounds of the invention in pure isomeric form, e.g. consisting of at least 90%, preferably at least 95% of a single isomeric form, as well as mixtures of these forms. Thus the compounds of the invention may be in the form of individual enantiomers or may be in the form of racemates or diastereoisomeric mixtures or any other mixture of the possible isomers (e.g. as derived from a racemic building block).
The compounds of the invention may be prepared by synthetic chemical procedures, including procedures similar to those which may be used for the synthesis of xcex1-amino acid peptides. Such procedures include both solution and solid phase procedures, e.g. using both Boc and Fmoc methodologies. Thus the compounds of formula I may be prepared by successive amide bond forming procedures in which amide bonds are formed between the xcex2-amino group of a first xcex2-amino acid residue or a precursor thereof and the xcex1-carboxyl group of a second xcex2-amino acid residue or a precursor thereof. The amide bond forming step may be repeated as many times, and with specific xcex2-amino acid residues or precursors thereof, as required to give the desired xcex2-peptide. Also xcex2-peptides comprising 2, 3 or more xcex2-amino acid residues may be joined together to yield larger xcex2-peptides. Cyclic compounds may be prepared by forming peptide bonds between the N-terminal and C-terminal ends of a previously synthesised linear xcex2-peptide.
xcex2-amino acids may be produced enantioselectively from corresponding xcex1-amino acids; for instance, by Arndt-Eisert homologation of N-protected xcex1-amino acids. Conveniently such homologation may be followed by coupling of the reactive diazo ketone intermediate of the Wolff rearrangement with a xcex2-amino acid residue.
Thus the invention includes a process for the preparation of a compound of formula I comprising Arndt-Eisert homologation of an N-protected xcex1-amino acid of formula VI 
wherein Pg, is an amine protecting group and R and R2 are as defined above, by reaction with diazomethane, e.g. in the presence of triethylamine/ethylchloroformate, to yield a diazo ketone intermediate of formula VII 
wherein Pg, and R and R3 are as defined above.
The invention also includes a process for the preparation of a compound of formula I comprising coupling of a diazo ketone of formula VII 
with a xcex2-amino acid of formula VIII 
wherein R and R3 are as defined above and Y is an O-protecting group, or with a xcex2-amino acid or xcex2-peptide residue of formula IX 
wherein R and R3, are as defined above, Pxe2x80x2g is an O-protecting group and p is 1, 2, 3, 4, 5, 6, 7, 8 or 9.
Any suitable reaction conditions or procedure may be used for the coupling reaction between the compounds of formulae VIII and IX. For example, the coupling reaction may be carried out in the presence of a silver catalyst, e.g. Ag benzoate in Et3N, with cooling, e.g. at a temperature of 0xc2x0 C. to xe2x88x9240xc2x0 C., in the dark under an inert atmosphere. Alternatively, for example, the coupling reaction may be catalysed by light, e.g. irradiation of the reaction mixture with a low pressure mercury lamp.
The compounds of formulae of the invention may be used to establish discrete compound collections or libraries of compounds for use in screening for compounds having desirable activities, in particular biological activities indicative of particular pharmaceutical uses.
Thus the invention also includes discrete compound collections (typically comprising from 2 to about 1000 compounds) and libraries of compounds (typically comprising from 20 to 100 compounds up to many thousands of compounds, e.g. 100,000 compounds or more) comprising pluralities of the compounds of the invention.
As will be appreciated the particular identity of the substituents R, R1, R2, R3 and X depends upon the choice of building blocks and reaction steps used for synthesis of the compounds of formula I. The substituents R, R1, R2, R3 and X may be chosen as desired to provide groups of related compounds having particular structural themes or to provide unrelated, structurally diverse compounds.
Compounds having desired biological activities may be identified using appropriate screening assays. For example the following screening assays may be used to screen for particular biological activities indicative of corresponding pharmaceutical uses.
Antiinflammatory and immunosuppressive activities of compounds of formula I are determined by means of the following and similar assays: the IL-1xcex2 secretion inhibition, LPS fever, cytokine release from THP-1 cells, and functional IL-1 antagonist assays and the assay of carrageenan induced paw edema in the rat (as described in EP 0606044 and EP 0618223); the macrophilin binding, Mixed Lymphocyte Reaction (MLR), IL-6 mediated proliferation, localised graft-versus-host (GvH) reaction, kidney allograft reaction in the rat, experimentally induced allergic encephalomyelitis (EAE) in the rat, Freund""s adjuvant arthritis, FKBP binding, steroid potentiation and Mip and Mip-like factor inhibition assays (as described in WO 94/09010, EP 0296123 and EP 0296122).
Central Nervous System (CNS) activity of compounds of formula I is determined by means of the following and similar assays: serotonin ID (5HT 10) receptor agonist assays including the method of Weber et al.(Schmiedeberg""s Arch. Pharmacol. 337, 595-601 (1988)) (and as described in EP 0641787)); 5HT3 receptor agonist assays (as described in GB 2240476 and EP 0189002); assays for activity in treatment of psychotic disorders and Parkinson""s Disease, such as the apomorphine induced gnawing in the rat assay and dopamine receptor (D1 and D2) binding assays (as described in GB 20206115 B); assays for dopamine receptor antagonist activity (in relation to schizophrenia and related diseases, as described in EP 0483063 and EP 0544240); assays for activity in relation to senile dementia and Alzheimer""s Disease (as described in EP 0534904); assays for activity in relation to cerebral ischaemia (as described in EP 0433239), and assays in relation to gastrointestinal motility such as the peristaltic reflex in isolated guinea pig ileum and assays of antiserotoninergic effects (specifically at the 5-HT4 receptors) (as described in EP 0505322)
Activity of the compounds of formula I in relation to bone and calcium metabolism is determined by assays as or similar to those described in WO 94/02510, GB 2218102B and WO 89/09786.
Activity of the compounds of formula I in relation to asthma and other allergic and inflammatory conditions is determined by the following assay procedures: the PDE isoenzyme inhibition, inhibition of eosinophil activation by formyl Met Leu Phe (f MLP), inhibition of TNFxcex1 secretion, inhibition of SRS-A production, bacterial endotoxin (LPS) induced lethality in the guinea pig, arachidonic acid induced irritant dermatitis in the mouse, relaxation of the human bronchus, suppression of SRS-A induced bronchoconstriction, suppression of bombesin induced bronchoconstriction, suppression of methacholine (MeCH) induced bronchoconstriction in the rhesus monkey and suppression of airways hyperactivity in the guinea pig assays (as described in European patent application No. 94810628.1 [EP 0664289], WO 94/12493 and GB 2213482).
Serine protease, e.g. Thrombin, inhibition activity of the compounds of formula I is determined using assays such as those described in WO 94/20526. Glycoprotein IIb/IIIa antagonist, activity of the compounds of formula I is determined using the assay procedures described by Cook et al. (Thrombosis and Haemostasis, 70(3), 531-539 (1993) and Thrombosis and Haemostasis, 70(5), 838-847 (1993)) Mxc3xcller et al. (J. Biol. Chem., Vol. 268, No. 9, 6800-6808 (1993)).
Anticancer activity of the compounds of formula I is determined by the anti tumour activity assay as described in EP 0296122 or by trial procedures, for instance as described in GB 2239178. Multidrug resistance (MDR) reversing activity is determined by the assays described in EP 0296122.
The relevant teachings of the patent documents and other publications referred to above is incorporated herein by reference. Compounds of formula I which have appropriate levels of activity in these assays are useful as pharmaceuticals in relation to the corresponding therapies or disease states.
Thus the invention includes compounds of formula I for use as pharmaceuticals and the use of a compound of formula I for the manufacture of a medicament for the. treatment of any disease associated with any of the assays hereinbefore described. The invention also includes the use of a compound of formula I as a pharmaceutical, and pharmaceutical compositions comprising an effective amount of a compound of formula I together with a pharmaceutically acceptable diluent or carrier.